Look at Star Trek films.The focus on them have been Kirk,Spock and lesser degree Mccoy In 6 original films.Picard and Data In NG,and Kirk and Spock In Altertate Timeline.Even the Avengers I saw as mostly focused on Tony Stark and Captain America

Days of future past will focus on Xavier and Magneto In 1960's and Wolverine In future.If Rogue(or less likely Kitty) Is time traveler then that would make her a focal character.
If they would go with Xavier switching minds between patrick stewert and James Mcavoy versions then future Xavier would be a focal character in future scenes.